This invention relates to cooled microelectronic systems and, more particularly, to a sensor system with an integral cryocooler that rapidly cools the sensor when placed into service.
In one type of imaging infrared sensor system, a microelectronic light sensor is deposited on a substrate. The substrate is supported on a cold-finger pedestal. Another end of the pedestal is cooled by a cooler such as a Joule-Thompson cooler. The light sensor achieves its most efficient operation and highest signal-to-noise ratio when cooled to a cryogenic temperature such as liquid nitrogen temperature or lower. The light sensor and the cold-finger pedestal are placed inside a vacuum enclosure which has a window facing the light sensor and through which light is admitted. The vacuum enclosure insulates the light sensor and cold-finger pedestal, and protects the light sensor.
When the sensor system is to be operated, the cooler is activated to cool the cold-finger pedestal and thence the light sensor to cryogenic temperature. Upon reaching the cryogenic operating temperature, the light sensor is activated. The output signal of the light sensor is provided to a display or to a computer for further processing.
Microelectronic sensor systems of this type are well known and widely used. One of their drawbacks, however, is that the time required to cool the light sensor from ambient temperature to its cryogenic operating temperature may be on the order of one minute. For some applications that cooldown time may be acceptable, but for other applications, such as military applications, it may be unacceptably long. Additionally, the light sensor is cantilever mounted on the end of the cold-finger pedestal, increasing the susceptibility of the signals to degradation due to vibration. There is also the desire to decrease the size and weight of the sensor system as much as possible.
Various techniques have been employed to increase the cooldown rate and to reduce the size and weight of the sensor system. However, there remains a need for an improved approach to cryogenically cooled sensor systems that overcomes the shortcomings while still providing the required low operating temperature and satisfactory performance of the light sensor.
This cooling problem has been posed in relation to sensors, but it is equally applicable to some other types of microelectronic systems that generate large amounts of heat during service, such as high-performance computer chips and microelectronic amplifiers. It may not be necessary to cool these microelectronic systems to cryogenic temperatures, but accelerated heat removal may be required to maintain the microelectronic systems within operating temperature limits.
Thus, there is a need for an improved approach to cooling a variety of microelectronic systems, some to cryogenic temperatures. The present invention fulfills this need, and further provides related advantages.
The present invention provides a microelectronic system in which heat is rapidly removed and the components of the microelectronic system are cooled. The cooling may be to a cryogenic temperature. The cooler is integral with the microelectronic system rather than being separate from it as in conventional cold-finger pedestal designs. There is a shorter path from the microelectronic system to the cold sink and fewer interfaces than in conventional coolers (and in some cases no interfaces), with less thermal impedance as a result. The microelectronic system is therefore cooled from a higher temperature to its service temperature, which may be a cryogenic service temperature, more rapidly than in conventional designs. The size and weight of the microelectronic system are reduced. In the case where the microelectronic system is a sensor system, performance of the sensor system is improved because the light sensor is not cantilevered at the end of an arm, so that there is less susceptibility to vibration.
In accordance with the invention, a sensor system comprises a substrate, a microelectronic device such as a light sensor or other chip supported on the substrate, and a cryocooler formed in and integral with the substrate.
In a preferred approach, the substrate is made of silicon. A microelectronic device is formed in the silicon substrate or other type of substrate material. The microelectronic device may generally be of any type. In one example, the microelectronic device may be a chip such as a silicon-based microcircuit (e.g., a microprocessor chip) or an amplifier chip for a computer or other application. In another example of interest, the microelectronic device in the form of a light sensor comprises a readout integrated circuit formed in and integral with the substrate, and a light detector supported on and electrically interconnected with the readout integrated circuit. The cryocooler is a Joule-Thomson cryocooler.
The cryocooler preferably comprises a gas inflow channel in the substrate, an expansion nozzle in the substrate, a nozzle inlet that receives a gas flow from the gas inflow channel, a nozzle outlet, and a gas outflow channel in the substrate that receives the gas flow from the nozzle outlet. There may additionally be an expansion volume in fluid communication with the nozzle outlet, so that the gas outflow channel is in fluid communication with the nozzle outlet through the expansion volume. The gas outflow channel is preferably countercurrent to the gas inflow channel. The gas inflow channel and the gas outflow channel may each be a spiral in plan view, or they may be of other shapes such as straight, curved but not spiral, serpentine, and the like. The substrate may have multiple layers. For example, the substrate may comprise a first layer and a second layer, with the gas inflow channel and the gas outflow channel in the first layer, the expansion volume in the second layer, and the microelectronic device integral with the second layer. The substrate may comprise three layers, with the gas inflow channel in the first layer, the gas outflow channel in the second layer, the expansion volume in the third layer, and the microelectronic device integral with the third layer. Other multilayer structures are possible. In the case where the light sensor includes the readout integrated circuit and the light detector, the readout integrated circuit is formed in the substrate, and the light detector is supported on the readout integrated circuit.
A method for cooling a microelectronic system comprises the steps of fabricating a microelectronic system by furnishing a substrate having a front side and a back side, depositing a microelectronic device onto the front side of the substrate, and microforming a cryocooler within the substrate between the microelectronic device and the back side of the substrate, or on the back side of the substrate. The method further includes introducing a pressurized gas into the cryocooler to generate cooling of the substrate and the microelectronic device readout integrated circuit, and operating the microelectronic device. The above-described embodiments may be used in conjunction with the method, and the features of the method may be used in conjunction with the above-described embodiments.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.